OBJECTIVE: To evaluate neuromuscular junctions (NMJ) in R98C Mpz mutant mice treated with IFB088, a specific inhibitor of Gadd34/Ppp1r15a phosphatase

BACKGROUND: The R98C mutation in myelin protein zero (MPZ) causes a severe early-onset form of Charcot-Marie-Tooth disease 1B (CMT1B) and a similar neuropathy in knock-in mice we previously demonstrated that IFB088, a specific inhibitor of the Gadd34/Ppp1r15a phosphatase, increased holding time of the mice on the accelerating rotarod, increased their grip strength and increased both motor and sensory conduction velocities. Prior studies have shown that abnormalities of the NMJ are early morphological features of rodent models of CMT. We wished to determine whether IFB088 provides neuromuscular junction (NMJ) morphological benefit in R98C MPZ mice, a model of CMT1B in which the unfolded protein response (UPR) contributes to the neuropathy.

METHODS: We performed a detailed NMJ morphology analysis of triangularis sterni muscle in treated and vehicle treated animals. The R98C MPZ heterozygous and wild type mice were fed with IFB088 or vehicle(saline) via gavage beginning at postnatal day 30(P30), continuing through 6 months of age (P180). Mice were evaluated clinically by rotarod, physiologically by nerve conduction studies and nerve morphology studies. Morphology analysis of immunohistochemistry at NMJ was performed for studies on 4-month-old and 6-month-old animals. Stack images were taken by confocal microscopy and measured by Image J software.

RESULTS: The percentage of fully myelinated neuromuscular junctions in the triangularis sterni muscle in R98C MPZ heterozygous mice IFB088 was increased, and demyelinated segments were shorter (P<0.05 by T-test and ANOVA) in mice treated with IFB088 in preterminal internodes of NMJ in 6-month-old animals.

CONCLUSIONS: These data, combined with prior behavioral and physiological studies demonstrate that IFB088 improves the neuropathy of R98C MPZ CMT1B mice, a model of CMT1B involving UPR activation.